Yes, how could I not get sucked in to write about the backbone of the GBMI (Great British Motorcycle Industry). I'm not sure what you find complicated Paul. Any business that made engines by the million and did so for sixty odd years will have an extensive history, Villiers no more so than any other.
I would suggest that to learn about Villiers you start off by looking at these particular websites and then come back with any specific questions afterwards.
Firstly,
www.historywebsite.co.uk/Museum/Engineering/Villiers/Villiers.htm The next site gives a potted preview of the Jack Sizer Villiers history, it is
www.users.globalnet.co.uk/~pattle/nacc/arc0596.htm Then my mate Ron Wileys attempt at
www.communitywebs.org/AdelaideHillsMotorRestorersClub?assets/dicks-articles/36-Villiers-engines-part-1.pdf and finally a Dutch site where the site owner has lifted Villiers id numbers from both Jack Sizers history and Roy Bacons "Post war Villiers singles and twins' and popped them in his site. This one is ww.hulsmannmotor.nl/Villiers_motornummers.html
All of the above will give you a pretty broad overview although far from complete. For example, one of my little amusements since Roy Bacon published his by far the most useful postwar Villiers history book is to track down Villiers ID numbers he doesn't list. I have about fifty so far.
As you can see, some of us can get quite sad with our little motorcycle obsessions. Luckily mine is just old Villiers two-strokes.
I look forward to your return when you have done your home work. A written examination is required.
Cheers,